Location: National Peanut Research Laboratory
2025 Annual Report
Objectives
Objective 1
Identify and integrate beneficial genes from disease-resistant peanut and wild peanut sources into genetically stable peanut germplasm.
Sub-objective 1A.
Screening for aflatoxin accumulation under laboratory conditions.
Sub-objective 1B.
Identification of disease resistance-associated genes and plant defense mechanisms.
Sub-objective 1C.
Integration of beneficial alleles from wild diploid Arachis species into genetically stable peanut germplasm.
Objective 2
Define specific defensive roles of peanut phytoalexins against Aspergillus spp. and other fungal pathogens and identify their genetic sources as potential resistance to fungal diseases and aflatoxin contamination.
Sub-objective 2A.
Determination of phytoalexin profiles in experimental and field seeds and search for new phytoalexins.
Sub-objective 2B.
Study of potential involvement of pegs in contamination of peanut seeds with aflatoxins.
Approach
Peanut (Arachis hypogaea) is one of the major food crops in the world. Most of the pathogens that attack peanuts are of fungal origin and are evident etiological factors of over 40 economically important peanut diseases. Aspergillus flavus and A. parasiticus are opportunistic fungal parasites that often invade peanut seeds and produce carcinogenic aflatoxins. Contamination of peanuts with aflatoxins is an important food safety issue and threatens the competitiveness of the United States agriculture in the world market. Aflatoxin monitoring and reprocessing of contaminated peanuts is a passive and costly practice to prevent aflatoxins from entering the food chain. Current peanut cultivars often demonstrate limited resistance to fungal pathogens. Therefore, wild peanut species have received substantial consideration as sources of disease resistance because the narrow genetic base of cultivated peanuts cannot provide the necessary levels of resistance to defend the peanut plant. A prospective approach to reduce disease pressure and aflatoxin contamination is to develop resistant peanut cultivars through introgression of beneficial genes and alleles from wild peanut species into elite cultivars. To achieve this goal, the first objective to identify and integrate beneficial genes from disease-resistant peanut and wild peanut sources into genetically stable peanut germplasm will use this approach. In conjunction with this objective, another promising strategy/second objective is to define specific defensive roles of peanut phytoalexins against Aspergillus spp. and other fungal pathogens and identify their genetic sources as potential resistance to fungal diseases and aflatoxin contamination. Both approaches will generate new knowledge on the mechanisms of peanut resistance to fungal invasion and a faster release of enhanced germplasm and cultivars. The ultimate goal of this project is to reduce peanut disease load and to develop improved germplasm. The beneficiaries of the successful accomplishment of the project goal are breeders and all segments of the peanut industry.
Progress Report
ARS Researchers at Dawson, Georgia made significant progress towards achieving Objective 1, Sub-objectives 1A, 1B, and 1C. Laboratory-based screening for aflatoxin quantification of 480 genotypes from in-house developed pre-breeding materials, identified prospective pre-breeding lines with null or lower than the U.S. permitted levels of aflatoxin B1. A set of 140 plants from these lines are currently grown in a greenhouse to full maturity and will be used for further evaluations to confirm their performance. A genome-wide single nucleotide polymorphism genotyping, performed on “de-novo” interspecific F1 hybrids and synthetic amphidiploids, allowed for the identification of parental line-specific alleles and potential diagnostic molecular markers for the selection of individuals with desirable traits. A gene expression dataset generated from peanut seeds that were challenged with Aspergillus flavus from 18 genotypes with varying aflatoxin accumulation profiles, provided a first insight into the genes and pathways that underlie the mechanisms of aflatoxin resistance in peanut. Pre-breeding efforts were initiated to transfer favorable alleles for resistance to aflatoxin accumulation and leaf spot diseases from two in-house developed amphidiploids into elite lines/cultivars. The project also contributed to the publication of the registration of two introgression lines with resistance to leaf spots and tomato spotted wilt virus.
Considerable progress has been made to achieve Objective 2, Subobjective 2A. A new concept of peanut seed challenging with toxigenic fungi was tested on hundreds of individual cotyledon cutouts. Compared to the existing method, the new method requires less time and materials used and is characterized by precise control of sample preparation (rehydrating and cutting) as well as by experimental parameters, including water activity levels and concentrations of fungal spores. We plan to further develop this promising method and use it in our future work. We continued obtaining important High-Performance Liquid Chromatographic quantitative profiles of fungal-challenged seed extracts from resistant and susceptible tetraploid peanut genotypes. The data were compared with genetic and genomic information obtained from the same seeds. Such an approach helped to ensure the correct selection of the genetic material.
Accomplishments
1. Developing pre-breeding materials for reduced pre-harvest aflatoxin accumulation and resistance leaf spot (LLS) diseases. Aspergillus flavus and A. parasiticus are opportunistic pathogens that invade peanut seeds causing accumulation of aflatoxins. The economic impact of aflatoxin in U.S. peanuts is significant. The industry invests substantial resources to ensure consumer safety, often in millions of dollars each year. Therefore, breeding for reduced aflatoxin accumulation is a high priority. ARS Researchers at Dawson, Georgia are utilizing wild peanut species and landraces to transfer favorable genes into cultivated peanut. Through interspecific hybridization, chromosome doubling, and advanced genomic analyses, the project developed fertile pre-breeding lines. Initial pre-breeding efforts were successful in obtaining first filial generation hybrids between these newly developed lines and cultivated peanuts, indicating their ability to interbreed with elite cultivars. Laboratory-based screening for aflatoxin resistance and field evaluations for leaf spots diseases, further identified and selected prospective introgression lines carrying the desirable target traits. Overall, this research generated key genetic resources for the development of germplasm with desirable traits, the essential raw material for peanut breeding to reduce pre-harvest aflatoxin accumulation and enhance resistance to leaf spots diseases.
2. Characterizing phenotype variants of Cercosporidium personatum, causal agent of peanut late leaf spot (LLS) disease, their morphology, genetics and metabolites. ARS scientists at Dawson, Georgia, discovered and reported (Sci. Rep. 15:1405) for the first time the production of anthraquinones (norsolorinic acid, averantin, averufin, averufanin, nidurufin, versicolorin B, and versicolorin A) in Cercosporidium personatum (CP), economically important causal agent of peanut LLS disease. These compounds are precursors of the known carcinogens, aflatoxin and dothistromin. The peanut industry loss due to the LLS exceeds $40,000,000/year. In a joint effort, the researchers characterized the morphology, genomes, transcriptomes, and quantitative chemical composition of the three morphotypes (RED, TAN, and BROWN) of the fungus as well as resistance of the morphotypes to xenobiotics. The scientists showed for the first time that different isolates of this pathogen, even those originated from the same spore, could have contrasting chemical profiles, and exhibit large variation whether growing in presence or absence of light. Chemical profiles indicate each CP morphotype could trigger different immune responses in the peanut plant, potentially hindering development of durable LLS resistance. In addition, we showed that different isolates of C. personatum could produce significantly different concentrations of ergosterol, a compound that at certain concentrations could trigger different immune responses in the plant and could be a confounding factor negatively affecting plant defense mechanisms. This fact also should be accounted for in breeding efforts toward LLS resistance.
Review Publications
Arias De Ares, R.S., Orner, V.A., Sobolev, V., Massa, A.N., Faustinelli, P.C., Walk, T., Lamb, M.C., Butts, C.L. 2024. Novel foodborne source of Xerochrysium xerophilum (Pitt) Pitt, raw peanuts stored at low moisture and high CO2. Journal of Stored Products Research. 108. Article 102381. https://doi.org/10.1016/j.jspr.2024.102381.
Arias De Ares, R.S., Cantonwine, E., Orner, V.A., Walk, T., Massa, A.N., Stewart, J., Dobbs, J., Manchester, A., Higbee, P.S., Lamb, M.C., Sobolev, V. 2025. Characterizing phenotype variants of cercosporidium personatum, causal agent of peanut late leaf spot disease, their morphology, genetics and metabolites. Scientific Reports. 15, 1405. https://doi.org/10.1038/s41598-025-85953-9.
Faustinelli, P.C., Massa, A.N., Soria, N.W., Lopez-Colomba, E., Suarez, P.A., Lamb, M.C. 2025. Determination of chlorophyll content in in vitro peanut leaves. Current Protocols in Plant Biology. 5, e70150. https://doi.org/10.1002/cpz1.70150.
Arias De Ares, R.S., Dobbs, J.T., Orner, V.A., Conforto, C., Rajo, A., Cazon, L.I., Sobolev, V., Power, I., Lamb, M.C., Massa, A.N. 2025. First metagenome- and metatranscriptome dataset of Thecaphora frezzii teliospores,assembly and annotation of a new bacterial genome. Data in Brief. 61(111779). https://doi.org/10.1016/j.dib.2025.111779.